The invention relates to a stator for a stepping motor of an electric watch comprising an elongated yoke member having a free end, a coil arm integrally formed on the other end of the yoke member and having a free end, an exciter coil arranged on the coil arm by being pushed onto the coil arm from the free end thereof, and also comprising a bridge member connecting the free ends of the yoke member and the coil arm, the yoke member with the coil arm and the bridge member hereby being flat elements made of a magnetizable sheet metal.
A stator of this type is known, for example, from French laid-open paper FR-OS 24 51 653. The construction of the stator plate of the known stator is advantageous in so far as it offers the possibility of pushing the finished coil, e.g. an exciter coil wound onto a coil core, onto the coil arm from its free end. This means that the coil may be produced on customary winding machines and need not be wound on the stator itself. The known stator uses a basically L-shaped bridge, the short arm of which has an inclined face butt-jointed to a corresponding inclined face of the yoke. The long arm of the bridge, which also has an inclined face, projects into the interior of the coil where its inclined face is butt-jointed to a corresponding inclined fact at the free end of the coil arm.
This known solution for the construction of a stator has the disadvantage that the magnetic path of the stator which must pass across the yoke, the coil arm and the bridge to close the magnetic circuit has a badly defined magnetic conductance, which is often too low, in the regions of the contact points between the bridge, on the one hand, and the yoke and the coil arm, on the other. The problems associated therewith are aggravated by the fact that the contact point between the coil arm and the long arm of the bridge is located in the interior of the coil and is not, therefore, visible when the bridge is assembled. This may result in inaccuracies during assembly of the known stator arrangement, in addition to the fundamental shortcoming resulting from the two butt joints. Any errors occurring during assembly will later impair the operation of the stepping motor, the rotor of which is generally arranged in a circular recess in the yoke. Moreover, the constructional design of the known stator has an additional disadvantage. The pointed ends of the various parts of the stator, which are usually punched form transformer sheets or the like, may entail the risk of injury to personnel during assembly and also increase the risk of the exciter winding of the coil being damaged by the sharp ends of the transformer parts if these are handled carelessly. This can result in, for example, a short-circuit in the coil or an interruption.
Proceeding on the basis of the state of the art and the problems discussed above, the object of the invention is to improve a stator of the type described at the outset such that a good, uniform magnetic conductance is maintained along the closed magnetic path of the stator.
This object is accomplished according to the invention, for a stator of the type described at the beginning, in that the coil arm is of a greater length than the exciter coil and that the bridge member rests flat on the free ends of yoke member and coil arm and overlaps regions of these elements to form an areal contact.